1. Field of the Invention
The present invention relates to techniques for processing radiology images, and more particularly to methods for automatically orienting electronically acquired radiology images.
2. Background Art
In radiology technology, X-ray images are acquired using a phosphor plate. The phosphor plate is exposed using the same X-ray generator that has been used traditionally with film. The phosphor plate is then read in a Computed Radiology (CR) machine, resulting in a digital image. The digital image can be transported over a network, stored, retrieved, viewed, and diagnosed electronically.
An electronic image has a well defined top, bottom, right side, and left side. The image is in a raster format scanned from top to bottom and from left to right. The pixels in the image appear in rows with the first row being at the top of the image and the pixels in raster order from left to right.
The patient may have many different orientations in the image. The patent's head may be at any of the four sides of the electronic image. Furthermore, the image may have been acquired with the patient facing out instead of in, resulting in a mirror image, shifting the right to the left. The same effect can be caused by inverting the orientation of the imaging cassette as the image is acquired.
A very large percent of the images acquired in a hospital are chest images. Another frequently acquired images is abdomen images. The rest of the images are miscellaneous hands, feet, arms, legs, pelvises, heads, and shoulders. The chest images and the abdomen images have a natural orientation. The chest images may be either front (PA or AP) or side (Lateral). The abdomen images are invariably front images. The chest images are likely to be more than 50% of the regular X-ray images collected in a hospital. With the abdomen images the number of images of the two types may approach 70% of the images in the hospital.
Organizing the images and orienting the images for display can require a large amount of time for the radiologist. With the images organized for viewing a typical radiologist will require from three to five minutes to read an exam and dictate a report. If the radiologist must organize the exam several minutes longer will be required. A chest exam with two images should be organized with the PA image on the first monitor and the lateral image on the second monitor. A radiologist can move the images from one monitor to the other in about thirty seconds. If the images are oriented randomly as they are when acquired, the mis-oriented images must be rotated and possibly flipped, adding another 15 seconds per image. The result will be a typical addition on the order of one minute to the reading time for the mis-oriented images. This process will add 20% to 30% to the reading time for the radiologist.
In many hospitals the images are arranged for the radiologist by a technician. The technician will move the images such that the PA and Lateral images are correctly ordered and will orient the images such that the head is at the top and the heart is on the right side of the image for the PAs. The orientation of the laterals is up to the hospital. The head is oriented at the top and the patient is typically oriented facing toward the right. Similarly, the abdomen images are arranged so that the patient's head is at the top of the image for viewing.
If the image can be properly oriented automatically, the technician effort can be eliminated and the rest of the adjustment of the viewing can be done by the radiologist with little waste of time. The radiologist will typically adjust the window and level in the process of reading the images, so little extra time is spent if the window and level are not adjusted to a starting place for the radiologists.
The result is that the technician effort can be eliminated if the orientation of the images can be done effectively.
In medical technology electronic image acquisition is relatively new in medicine. While some digital images have been available, the bulk of the standard X-ray images have been on film. Consequently, there is no general background of medical processing of images to determine orientation.
However, the processing of non-medical digital images has had many image recognition and image orientation procedures developed. In automatic target recognition there have been neural network techniques developed that recognize generic shapes such as vehicles or aircraft. These algorithms must recognize the shapes regardless of orientation. Some of the algorithms recognize the orientation before attempting to recognize the shape.
Optical character recognizers must recognize the orientation of the characters that are being recognized. Typically the orientation is generally known as upright with ad-hoc techniques used to recognize the fine adjustments in the orientation necessary to proper character recognition.
A general technique useful for recognizing an isolated shape measures the moments of the image. The first moment in the X and Y direction can be used to determine the "center" of the image. A measure of the angular moment about the center can be used to find a center line. Further moments about the center line can be used to find bulges and other attributes of the image.
The difficulty with these schemes is that they generally do not apply to the medical images. The neural network approaches might be made to work, but will be complex and clumsy, requiring a large amount of computation. The techniques applied to character recognition cannot be adapted to medical images, since the techniques apply to objects that are already upright and for which the techniques are very ad-hoc applied to characters. The medical images generally do not have an isolated object to identify. The chest and abdomen images fill the full image. The simple measurement of moments will not be sensitive to the location of the heart in the chest cavity.
References relating to the technology of processing optically obtained digital medical images includes the following U.S. Patents.
U.S. Pat. No. 4,630,203 issued Dec. 16, 1986 to Szirtes entitled Contour Radiography: A System For Determining 3-Dimensional Contours Of An Object From Its 2-Dimensional Images describes a method and apparatus for reconstructing the three-dimensional coordinates of an identifiable contour on an object without relying on markers or pre-existing knowledge of the geometry of the object. Two X-ray sources irradiate an object possessing a radiographically identifiable contour and then the two images of the contour are projected onto an X-ray film at spaced locations on the film plane. These images are digitized by the tracing of the image curves with a cursor or some other means thereby establishing the coordinates of an arbitrary number of image points. Then the coordinates are processed with the spatial coordinates of the X-ray source to determine the three-dimensional coordinates of their originating space-point on the contour. In this way the three-dimensional coordinates of the contour are determined. The three-dimensional coordinates are then processed to visually display the reconstructed contour.
This patent is different from the present invention is that the contour radiology requires two x-ray films of the same object to be recorded simultaneously. Furthermore, the geometry of the data acquisition has to be pre-determined. Our algorithm is applied to X-ray films which represent a single projection of an object. The decision of the image orientation does not rely on the priori knowledge of the collection geometry.
U.S. Pat. No. 5,570,430 issued Oct. 29, 1996 to Sheeham et al. entitled METHOD FOR DETERMINING THE CONTOUR OF AN IN VIVO ORGAN USING MULTIPLE IMAGES FRAMES OF THE ORGAN discloses a method for automatically evaluating image data taking over a sequence of image frames to determine a contour of a left ventricle (LV). The sequence of image frames are converted to digital data that identify a gray scale value for each pixel in each image frame. Using probability, an initial LV region is estimated based upon previously determined priori parameters that are derived from processing manually drawn contours of the LV in other hearts, for the sequence of image frames being analyzed. The initial estimate of the LV region is refined using motion constraints, which are also derived from training data determined from the manually drawn contours of other hearts. An LV region is estimated and its coordinates are extracted for use in applying global shape constraints that provide a more accurate LV boundary estimate for the region around an apex of the left ventricle. Consistency, yielding an accepted estimate, or warning that the estimates are unreliable. The resulting automatically determined contours of each image frame can be displayed after the image data are produced.
This patent is different from the present invention because the 3-D contours of a left ventricle have to be determined from a series of 2-D image frames. In order to perform a 3-D image reconstruction, the image orientation of each 2-D frame has to be the same. The algorithm described in this patent does not address the automatic image orientation. It is assumed that images from frame to frame are aligned, and therefore, this reference is distinct from the present invention.
U.S. Pat. No. 5,574,763 issued Nov. 12, 1996 to Dehner entitled COMPUTED TOMOGRAPHY APPARATUS discloses a computed tomography apparatus which enables an optimum examination of the small intestine region, having a patient support which permits a scan to be conducted of a patient with the patient in an upright, slightly tilted, position, and a control unit containing the x-ray source and detector at the same angle relative to said patient support for all positions of the patient support during a scan. A three-dimensional image reconstruction ensues such that, given a contrast agent fill of hollow organs, the hollow organ is computationally sliced, a contrast agent trunk is computationally removed and the inside of the hollow organic is thus displayed.
This patent relates to an apparatus of computed tomography to enable an optimum examination of the small intestine region. It does not involve in the algorithm of automatic image orientation and is distinct from the present invention.
U.S. Pat. No. 5,421,331 issued Jan. 6, 1995 to Devito et al. entitled AUTOMATIC IDENTIFICATION OF THE LONG AXIS OF THE LEFT VENTRICLE FROM NUCLEAR MEDICINE SPECT DATA FOR USE IN MYOCARDIAL PERFUSION STUDIES discloses a technique wherein the long axis of the left ventricle is automatically identified by identifying, and correlating, local minima and maxima in images of slices of the left ventricle. Initially, the left ventricle is identified within a representative transverse slice of the left ventricle. The centerline of this slice is automatically computed and used as a reorientation axis, along which another (sagittal) slice of the left ventricle is reconstructed. The centerline of this sagittal slice is automatically computed, and is the long axis of the left ventricle.
This patent automatically identifies the long axis of the left ventricle from a singe photon emission computed tomography (SPECT) and is distinct from the present invention because the algorithm of the present invention does not require the identification of the long axis of the left ventricle in order to determine the image orientation of either chest x-ray or abdominal images.
U.S. Pat. No. 5,429,135 issued Jul. 4, 1995 to Hawman et al. entitled DETERMINING THE DEPTH OF AN ORGAN WHICH IS THE SUBJECT OF A NUCLEAR MEDICINE STUDY USING ONLY PLANAR IMAGE DATA discloses a technique wherein two planar nuclear medicine images of a target organ are acquired using a focusing collimator at two different heights. As automatic landmark associated with the target organic is computer-identified in each of the images, and the depth of the target organ is determined geometrically using the differences in size between the images of the identified landmark and the differences in height.
This patent is different from the present invention because it determines the depth of an organ by acquiring two planar nuclear medicine images using a focusing collimator at two different heights. The present invention determines image orientation with a single projection of an X-ray film.
U.S. Pat. No. 5,494,041 issued Feb. 27, 1996 to Wilk entitled METHOD FOR USE IN SURGICAL OPERATION discloses a system for use in performing surgery including a video camera for generating a video signal encoding an image of organs of a patient, a display operatively connected to the video camera for displaying the image in response to the video signal, and an identification device operatively connected to the video camera for automaticallly analyzing the video signal to identify organs in the image. The identification device is operatively connected to the display for displaying symbols on the display to identify at least one of the organs in the image.
The sensor used in this patent is a video camera rather than x-ray, sensor of the present invention. The algorithm described in patent recognizes gall bladder and bile duct, which are not relevant to the algorithm of the present invention. Furthermore automatic image orientation process is not mentioned in this patent. The image orientation is assumed to be known before the recognition of gall bladder and bile duct. Therefore, this patent is distinct from the present invention.
U.S. Pat. No. 5,528,042 issued Jun. 18, 1996 to Haeuman entitled RETROSPECTIVELY DETERMINING THE CENTER OF ROTATION OF A SCINTILLATION CAMERA DETECTOR FROM SPECT DATA ACQUIRED DURING A NUCLEAR MEDICINE STUDY discloses a technique wherein tow conjugate views of a patient are acquired during a SPECT nuclear medicine study. A common anatomical features is identified in the views. Based on the differences in location of the common feature in the views, the center of rotation ("COR") of the detector during the study can be calculated after the study has been concluded. This COR can then be used during image reconstruction to determine the location at which each filtered view is backprojected. This patent requires two conjugate views of the body of a patient in order to automatically determine the center of rotation of a scintillation camera detector. The present invention, on the other hand, determined the orientation of an image of a patient from a single projection and is distinct from the patent.